Abstract 4778: Epigenetic modulation of colorectal cancer cells for cancer-testis antigen-targeted immunotherapy

Abstract

Abstract Cancer-testis (C-T) antigens represent attractive potential targets for cancer immunotherapy due to their limited expression in normal somatic tissues and their widespread expression in malignant cells of diverse histologies. The utility of C-T antigens for immunotherapy of colorectal cancer (CRC), however, is limited because expression of C-T genes is repressed in most CRC cells by hypermethylation. We investigated whether treatment of CRC lines with the hypomethylating agent 5-aza-2′-deoxycytidine (DAC) could induce C-T gene expression in CRC cells and thereby sensitize them to recognition by CD8+ cytotoxic T lymphocytes (CTL) specific for the highly immunogenic C-T antigen NY-ESO-1. A panel of CRC and primary dermal fibroblast lines was cultured with DAC or medium alone for 48 hours followed by culture with exposure to interferon γ (IFNγ) or medium alone for an additional 48 hours. After the treatment period, cells were harvested for collection of RNA, DNA, and protein; studied with flow cytometry for analysis of MHC class I and II expression; and tested for recognition by HLA-A*0201-restricted CTL specific for NY-ESO-1157–165 in a 51Cr release-cytotoxicity assay. Quantitative RT-PCR analysis of the expression of 20 C-T genes in untreated and DAC-treated cells using a custom PCR array showed that the majority of C-T genes were expressed at low levels in untreated CRC cells but were induced in most CRC cell lines by DAC exposure. Fibroblasts did not show any significant C-T gene expression with or without DAC treatment. Western blot analysis for NY-ESO-1 expression confirmed that DAC induction of NY-ESO-1 transcription was also associated with increased protein expression. DAC-treated HLA-A*0201+ CRC lines were also recognized by CD8+ HLA-A*0201-restricted NY-ESO-1-specific CTL. CTL recognition was enhanced when the cells were treated with IFNγ in combination with DAC, with the most significant effect seen in CRC cells with low baseline expression of MHC class I molecules. These data suggest that epigenetic modulation with DAC or related agents could be used to selectively induce expression of C-T antigens in CRC cells and thereby make them susceptible to C-T antigen-directed immunotherapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4778.